1. Field of the Invention
The present invention is related to a microstrip antenna transceiver, and more particularly, to a microstrip antenna transceiver which is capable of switching polarizations.
2. Description of the Prior Art
Satellite communication has advantages of huge coverage and no interference caused by ground environment, and is widely used in military applications, detection and commercial communications services, such as satellite navigation, a satellite voice broadcast system or a satellite television broadcast system. Nowadays, many electronic devices, such as smart phones, tablet personal computers, and so on can receive satellite signals via an external antenna. In general, the frequency of satellite signals ranges from 1.467 GHz to 1.492 GHz and two orthogonal signals are provided within the band at the same time, wherein one of the orthogonal signals is a left-handed polarized signal and the other is right-handed polarized signal. Therefore, a left-handed polarized antenna module and a right-handed polarized antenna module are required to receive the two orthogonal signals. However, practically, an electronic device does not handle the two orthogonal signals at the same time and only selects one. Moreover, two independent antenna modules occupy much space and increase the cost, so that the left-handed polarized antenna module and the right-handed polarized antenna module can be combined to one antenna module.
Please refer to FIG. 1, which is a schematic diagram of an antenna transceiver 10 according to the prior art. The antenna transceiver 10 is a switchable antenna transceiver with left-handed and right-handed polarizations and comprises a first switch 100, a second switch 102, a hybrid circuit 104 and a patch antenna 106, wherein the patch antenna 106 has vertical and horizontal space symmetry. The hybrid circuit 104 has four transmit ports P1-P4, in which the transmit ports P1 and P4 respectively connect to the first switch 100 and the second switch 102, and the transmit ports P2 and P3 respectively connect to the patch antenna 106 with vertical and horizontal polarizations.
In brief, for the transmitting operations, the first switch 100 and the second switch 102 control a signal S to enter the hybrid circuit 104 via the transmit port P1 or P4. The hybrid circuit 104 equally partitions the signal S into two transmit signals with a phase difference of 90 degrees, and follows to transmit the two transmit signals to the patch antenna 106. Then, the patch antenna 106 generates a vertically polarized signal SV and a horizontally polarized signal SH and radiates the vertically polarized signal SV and the horizontally polarized signal SH on the air. The patch antenna 106 has two feeding holes so that the two transmit signals equally partitioned from the signal S enter the two feeding holes to generate vertically polarized and horizontally polarized electromagnetic fields. Besides, since the vertical and horizontal spaces of the patch antenna 106 are symmetric, the energy of the vertically polarized signal SV and the horizontally polarized signal SH are not mutually affected. In other words, the patch antenna 106 has high isolation between the two polarized signals. In addition, the phase difference of the outputted signals from the transmit ports P2 and P3 is 90 degrees, so that the antenna transceiver 10 can generate a left-handed polarized or right-handed polarized antenna pattern. In detail, due to the characteristics of the hybrid circuit 104, when the signal S enters the hybrid circuit 104 via P1, the signal S has less energy reflected back to the transmit port P1 and less energy entered into P4. Therefore, the hybrid circuit 104 can equally partition the signal S with the 90-degree phase difference and transmit the equally partitioned signals to the patch antenna 106 via the transmit ports P2 and P3. Since the phase of the outputted signal via the transmit port P2 leads 90 degrees to that of the outputted signal via the transmit port P3, the patch antenna 106 can respectively generate the vertically polarized electromagnetic radiation and horizontally polarized electromagnetic radiation after receiving the outputted signals via the transmit ports P2 and P3, and further generate the left-handed polarized antenna pattern. For the same reason, if the signal S enters the hybrid circuit 104 via the transmit port P4, the hybrid circuit 104 can also equally partition the signal S into two signals and transmit the two signals to the patch antenna 106 via the transmit ports P2 and P3. Since the outputted signal via the transmit port P2 lags 90 degrees to the outputted signal via the transmit port P3, the patch antenna 106 can respectively generate the vertically polarized electromagnetic radiation and horizontally polarized electromagnetic radiation after receiving the outputted signals via the transmit ports P2 and P3, and further generate the right-handed polarized antenna pattern. In addition, the first switch 100 and the second switch 102 are used for controlling the transmit ports which the signal enters, to further control the antenna pattern generated by the antenna transceiver 10.
For receiving operations, the antenna transceiver 10 can also control the transmit port P1 or P4 to transmit the left-handed polarized or right-handed polarized signal received from the patch antenna 106 to a backend circuit module (which is not illustrated in FIG. 1) via the first switch 100 and the second switch 102. Besides, in comparison with the transmitting operations, the first switch 100 and the second switch 102 should rotate 180 degrees to conform the signal transmission direction.
As seen above, the conventional antenna transceiver 10 has high isolation for two orthogonal signals. However, the length and width of the hybrid circuit 104 need to be ¼ wavelength in order to perform the hybrid circuit, so that the hybrid circuit requires large plate area and the cost is increased for the low frequency of the present satellite signals. Therefore, how to reduce the cost of the antenna and handle the two orthogonal signals at the same time becomes a goal in the industry.